POSITIONING AND ENERGY RESPONSE OF PET BLOCK DETECTORS WITH DIFFERENT LIGHT SHARING SCHEMES

Two state-of-the-art modular PET block detectors using either discrete or pseudo-discrete BGO crystals coupled to two dual PMTs, utilizing different light sharing schemes, were evaluated. Both detectors were approximately 30 mm thick, while each element of the GE 6 x 6 block detector was 4 mm x 8.4 mm, and each element of the CTI 8 x 7 block detector was 2.8 mm x 5.8 mm. In addition to measurements with gamma sources, the detectors were also irradiated with a Sr/Y-90 beta source to evaluate the performance of the block detectors without inter-element scatter of annihilation photons. The best and worst energy resolutions of individual elements at 511 keV were 21.8% and 44.2% for the GE detector, and 22.7% and 42.5% for the CTI detector. The peak to valley ratios in the detector identification ratio histograms were generally better than 3 to 1. Measurements with beta sources indicate that light sharing in both detectors is a large component of event mispositioning along with inter-detector scatter of the annihilation photons.